In an internal combustion engine, such as a diesel engine, carbon from the combustion process can build up on the land of the piston above the upper compression ring. The carbon build-up typically does not form uniformly due to dimensional variations between the piston and the cylinder sleeve, non-uniform heat distribution and secondary motion of the piston. Excessive carbon build up may lead to problems characteristic of current commercial internal combustion engine piston-cylinder assemblies, namely, excessive crevice volume, premature ring fatigue failure, and excessive blow-by of fluids or induced oil combustion. Blow-by or migration of combustion gases or fluid oil past the piston rings is a continuous problem for piston assembly design. Blow-by of combustion gases to the crank case reduces engine compression and robs the engine of its designed power. Therefore, it is necessary and desirable to prevent these potential issues, as well as, remove any carbon deposits on a regular basis.
Carbon build-up has been dealt with, for example, by increased clearance between the top land of the piston and the cylinder sleeve and reduced oil consumption through refinements in the piston and piston design rings. Additionally, a carbon scraping ring or anti-polishing ring helps to scrape the carbon that builds-up on the top land of the piston. However, the carbon scraping ring still has to provide clearance between the ring and the piston to allow for thermal expansion, deformation due to pressure load, the back and forth motion of the piston (piston secondary motion), and the non-uniform heating to the piston.
Thus, there is a need for effective prevention and removal of carbon build-up while addressing the potential issues described above. The present device provides a carbon scraping ring or anti-polishing ring having an abradable coating applied thereto. The abradable coating provides a surface that will intentionally wear to the shape created by the motion of the piston within the cylinder liner sleeve regardless of the dimensional variation in the piston and/or cylinder sleeve, as well as, any variation in operating conditions. The abradable coating reduces the clearance between the carbon scraping ring and the piston, while creating an improved fit having a substantially zero clearance between the piston and the cylinder sleeve and carbon scraping ring. The present device prevents carbon build-up and facilitates removal of carbon deposits on the top land of the piston, as well as, reduces lube oil consumption and improves the consistency of the combustion process.